Distant star’s death throes give glimpse of sun’s future

Washington  A cloud of water vapor discovered around a distant dying star gives astronomers a glimpse of what may happen to the Earth and its sister planets when the sun dies.

The finding also suggests anew the possibility of life-supporting planets elsewhere in the universe, astronomers said Wednesday.

This image released by the Smithsonian Astrophysical Observatory
shows an aging star with a bigger mass than the sun. Astronomers
have found a cloud of water vapor around the distant dying star.

Gary Melnick of the Harvard-Smithsonian Center for Astrophysics said the star, called CW Leonis, is "the perfect laboratory for dissecting a dying solar system."

Melnick told a news conference the discovery marks the first time that a solar-system type of water cloud has been found around a star other than the sun, supporting the theory that there could be life elsewhere in the universe because liquid water is considered essential for life.

Melnick, co-author of a study appearing today in the journal Nature, said that the Submillimeter Wave Astronomy Satellite detected a vast amount of water vapor around CW Leonis, a star some 500 light years from Earth. A light year is about 6 trillion miles.

"What we have measured is the gaseous water emission resulting from the vaporization of a large number of icy bodies in orbit around the aging star," Melnick said.

He said CW Leonis was 1.5 to 4 times more massive than the sun. When such a star burns up all of its nuclear fuel, its superheated atmosphere suddenly expands. Melnick said that CW Leonis has now ballooned to a radius of about 483 million miles, approximately the distance of Jupiter from the sun.

Everything within that expanded sphere has now been burnt to crisp and the heat is melting a vast population of icy, comet-like bodies that circle in the far outer reaches of the CW Leonis system, Melnick said.

David Neufeld, a Johns Hopkins University astronomer and co-author of the study, said CW Leonis is a carbon star, a stellar body that has more carbon than oxygen. Such stars usually have virtually no water, since its sparse oxygen atoms are typically tied up with the abundant carbon to make CO2.

Instead, Neufeld said that CW Leonis has about 10,000 times more water than would be expected of a carbon star, based on the satellite observation data.

"The only logical explanation is that the water comes from a collection of icy bodies that are orbiting around the star and are evaporating because of the star's great power output," Neufeld said.

Melnick said the discovery boosts the belief that there may be life on planetary bodies orbiting stars beyond the solar system.

Since water vapor has been detected in a distant envelope around the star, he said, "it stands to reason that liquid water once existed in bodies close to the star.

"Since water is vital for life, (this) bolsters the possibility that a life-sustaining environment did exist outside our solar system," he said.

But if it ever did exist, said Melnick, it is gone, burned to a crisp by the dying throes of CW Leonis.

That is the eventual fate of the sun and the Earth, said Alan Bunner, science director of a NASA division studying the structure and evolution of the universe.

"Sometime in the future, about 6 billion years from now, our sun will burn up its nuclear fuel supply and expand to about the orbit of the planet Earth, sizzling and evaporating everything in its path," Bunner said.